The present invention is directed to methods and apparatus for decoding multiplexed, multi-type image information from a data stream, to enable printing in an optimum manner.
In U.S. patent application Ser. No. 07/696,681, a method for encoding data at a printer controller prior to printing is described. In that arrangement, all the possible combinations of line art and pictures may be synthesized using three gray or color multi-bit signals; two flat or Constant Colors in a scan picture; and two control signals; a high resolution binary Mask and a multi-bit instruction stream. A Constant Color is a color whose value is the same for all pixels, unlike the color defined by a scanned picture. A typical line art image is made up of a limited number of Constant Colors. Because color of text is usually constant or changes seldom along a scan line, a high resolution byte map of a text image on a flat color background can be synthesized from a high resolution binary Mask signal describing the filled out line of the text, and the two multi-bit Constant Color signals, describing the gray or color values of the text and of the background on which the text is set. By substituting a scanned picture signal for one of the Constant Color signals, the result is a high resolution text image overlaid on a scanned picture. Because the background for the text can be either a Constant Color or a scanned picture, an instruction would indicate which of the two it is.
Along the scan line, the system can merge these three elements: the two Constant Colors and the scan picture, selecting between them using a multiplexer under the control of the binary Mask and the instruction to produce a high resolution, multi-bit video signal which would be passed to the output device via a look up table for tone scale mapping and a register. The resulting video signal could be used to drive a gray scale display device such as a monitor, a gray scale printer, or a binary printer via halftone generator. Each of these signals could have a different spatial resolution or content along a scan line. The constant or flat colors change infrequently, although high precision is needed to specify the transitions. The scanned image has a medium spatial resolution and the binary Mask would have a high spatial resolution.
Using separate components or signals from which the final page image can be simply and easily synthesized has the advantage that the storage format can be optimized for each signal. Because the cost in colors and instructions are the same or change seldom along the scan line, they are candidates for run length encoding. The binary Mask can be stored compactly using any of the currently available binary compression algorithms, and the scanned picture can be stored using compression algorithms designed for gray scale image data.
U.S. Pat. No. 4,760,463 to Nonoyama et al. discloses an image scanner including an area designating section for designating a rectangular area on an original and a scanning mode designating section for designating an image scanning mode within and outside the rectangular area designated by the area designating section. Rectangular areas are defined by designating the coordinates of an upper left corner and a lower right corner. Subsequently, counters are used for each area boundary, to determine when the pixel being processed is within a specific area.
U.S. Pat No. 4,780,709 to Randall discloses a display processor, suitable for the display of multiple windows, in which a screen may be divided into a plurality of horizontal strips which may be a single pixel in height. Each horizontal strip is divided into one or more rectangular tiles. The tiles and strips are combined to form the viewing windows. Since the tiles may be a single pixel in width, the viewing window may be arbitrarily shaped. The individual strips are defined by a linked list of descriptors in memory, and the descriptors are updated only when the the viewing windows on the display are changed. During generation of the display, the display processor reads the descriptors and fetches and displays the data in each tile without the need to store it intermediately in bit map form.
U.S. Pat. No. 4,887,163 to Maeshima discloses an image processing apparatus having a digitizing unit capable of designating desired areas in an original image and effecting the desired image editing process inside and outside the designated areas. A desired rectangular area is defined by designating two points on the diagonal corners of the desired rectangular area. During scanning, a pair of editing memories are used interchangeably to enable, first, the editing of thresholded video data from a CCD and, second, the writing of editing information for use with subsequent video data. The editing memories comprise a memory location, one byte, for each CCD element, said location holding image editing data determining the editing process to be applied to the signal generated by the respective CCD element.
U.S. Pat. No. 4,951,231 to Dickinson et al. discloses an image display system in which image data is stored as a series of raster scan pel definition signals in a data processor system. The position and size of selected portions of an image to be displayed on a display screen can be transformed, in response to input signals received from a controlled input device. The display device includes a control program store which stores control programs for a plurality of transform operations, such as rotation, scaling, or extraction.
In the Canon CLC-500 digital color copier, introduced in 1989, provision is made to treat detected text with a high frequency halftone optimizing process, and to treat pictorial images with a low frequency halftone optimizing process.
The above-cited references are incorporated by reference for their teachings.